Various techniques have been used in the past to detect which inkjet printhead nozzles are functioning satisfactorily, and then doing recovery procedures to re-activate nozzles prior to doing a printout. In today""s printer world, throughput and print quality are somewhat contradictory goals. Nevertheless it may be possible to achieve both goals with a simple technique for monitoring nozzle functionality.
A nozzle detection test pattern has been developed which can be sensed by an optical sensor located on an inkjet printer carriage. By having the same nozzle print ink drops on multiple pixels to form a single thickened test line or module of a test pattern, during multiple passes of the printhead, it is possible to thereafter scan across such test line and automatically determine by the light contrast ratios which nozzles are not firing properly. A green light LED is used to illuminate magenta, cyan and black test patterns as they are being sensed, and a blue light LED is used to illuminate a yellow test pattern as it is being sensed. A separate test pattern is used for each printhead ink color. The test pattern constitutes six rows with forty test lines or modules on each row for a printhead having 240 active nozzles.